How do binary cycle power plants reduce air emissions?

Binary cycle power plants reduce air emissions by utilizing a closed-loop system that prevents geothermal fluids from being released into the atmosphere.1

In this design, geothermally heated water is pumped through a heat exchanger to transfer its thermal energy to a secondary working fluid, such as ammonia or hydrocarbons, which has a lower boiling point. This secondary fluid vaporizes and drives the turbine-generator set before being recondensed and cycled back through the system. Because the geothermal water never comes into contact with the turbine and remains contained within a sealed pipe network, the process effectively eliminates the release of gases that might otherwise escape in other types of geothermal power generation. Consequently, this closed-loop configuration produces no air emissions.21